As known in the art, a secondary battery refers to a battery capable of being charged and discharged, unlike a primary battery which is not possible to be charged.
As an example, a low capacity battery in which one battery cell is packaged in a pack form has been mainly used in small portable electronic devices such as a portable terminal, a note book, a computer, and a camcorder. As another example, a large capacity secondary battery in which a plurality of battery cells are connected in series or in parallel has been used in devices requiring high power, for examples, power supply for driving motor of an electric vehicle, and the like.
The secondary battery is possible to be manufactured in various shapes. As representative examples, the secondary battery is manufactured in a pouch-shape, a cylindrical shape, and a prismatic shape, and the like, Among them, the pouch type secondary battery is relatively free in view of a shape, and has a light weight, to be widely used in portable electronic devices requiring slimness and lightweight in recent years, and in an electric vehicle, and the like, in addition thereto.
FIG. 1 is a perspective view schematically showing a general pouch type lithium secondary battery.
Referring to FIG. 1, the general pouch type lithium secondary battery (1) is provided with a pouch packing material (hereinafter, referred to as a “pouch” 10) that is sealed along an edge. The pouch 10 includes a thin metal film and insulating films attached on both surfaces thereof to be freely bendable.
In addition, electrode laminates (not shown) are embedded in the pouch 10, and in order to embed the electrode laminates in the pouch 10, a predetermined space part for accommodating the electrode laminates may be formed in an inner portion of the pouch 10.
Meanwhile, a pair of electrode tabs 20 and 30 protrude toward an outer portion of the pouch 10, and these electrode tabs 20 and 30 may be electrically connected to the electrode laminates embedded in the pouch 10. However, the general pouch type lithium secondary battery further includes a gas chamber separately, in order to remove gas generated in a pre-charge process after an electrolyte is injected. In addition, when the gas is removed by a degassing process, it is required to remove the gas chamber and to reseal an open region. Accordingly, there is possibility of causing problems such as scattering of electrolyte, sealing defect, insulation resistance defect, and the like, such that a large amount of time is required for optimization of process conditions.
In addition, in the general pouch type lithium secondary battery, gas may be generated in a deterioration process. Here, when an amount of the gas generated by the deterioration process is more than a predetermined amount of the gas, appearance deformation of the pouch may be caused. As a result, the electrode laminates accommodated in the inner portion of the pouch are out of an initially arranged state and disorderly arranged, and in a worse case, short-circuit may occur therebetween to cause smoke or ignition. In spite of the above-described problems, a cell obtained after the resealing process is finished is completely blocked and sealed from the outside, such that additional injection of the electrolyte is hardly achieved, and it is difficult to discharge the gas that is generated by the deterioration process to the outside.
Korean Patent Laid-Open Publication No. 10-2013-0102807 (Publication Date: Sep. 23, 2013) which is a relevant prior art discloses a lithium polymer secondary battery.